:whs:
6637 intake--- $100
Exhaust--- $350-600
Guages--- $200-1000
Those mods aren't "power" mods but, are a very good investment on these trucks.
Next you'll want to get a TS chip with custom tunes and custom tunes only. Talk to some of the site sponsors, visit their sites, call them, pm them or whatever and decide which ones you think will fit you best.
My choices include, Matt @ Gearhead, Power Hungry Performance (PHP), Diesel Performance Plus, and Tyrant Diesel.... There are a lot more to choose from and they all have their advantages but those listed are the ones I've tried and I liked them all.
A custom tuned chip will run you between $250 and $500.
After that, well then it gets expensive.
If you have more questions, ask away, this place has more knowledge than any two places combined.